chore: scaffold .NET solution structure for Phase 6

Creates the four-project .NET 10 solution (ZB.MOM.NatsNet.slnx):
- ZB.MOM.NatsNet.Server: main library with MEL, BCrypt.Net-Next, IronSnappy
- ZB.MOM.NatsNet.Server.Host: console host with Serilog + Microsoft.Extensions.Hosting
- ZB.MOM.NatsNet.Server.Tests: xUnit 2.9 / Shouldly / NSubstitute / BenchmarkDotNet
- ZB.MOM.NatsNet.Server.IntegrationTests: same test stack, separate project

Also adds Phase 6 porting plan and task-tracking JSON.

dotnet/tests/ZB.MOM.NatsNet.Server.Tests/UnitTest1.cs

@@ -0,0 +1,10 @@
+namespace ZB.MOM.NatsNet.Server.Tests;
+
+public class UnitTest1
+{
+    [Fact]
+    public void Test1()
+    {
+
+    }
+}